This invention relates generally to diffraction gratings and is specifically directed to a method and apparatus for generating diffraction grating sections without first having to generate full size diffraction gratings on large circular blank substrates.
One method of generating circular variably-spaced (reflective) diffraction gratings is by ruling techniques using a diamond or other ruling means in a computer and interferometer controlled circular ruling engine. This method is used to generate on-axis "diffractive optics" for optical null testing and other applications. In this ruling engine, the blank grating substrate is continuously rotated on an air bearing table and the ruling means is moved radially, either continuously to produce a spiral groove, or in steps to produce circular grooves.
However, in many applications, the only part of the grating that is required is an off-axis section which means that a full grating must first be generated on a large blank which is excessively large and expensive. when only a part is needed and where the required section is then extracted afterwards by cutting or replication. These methods are wasteful and time consuming. FIG. 1 illustrates such a circular finished master grating on a full size circular substrate 10 with rulings 12 (only partly shown) and an off-axis section 14 that is cut from the finished product.